This invention relates to methods and apparatus for the separation of contaminant materials from gas-liquid and/or gas solid aerosols or other gas-liquid mixtures and their application to certain types of machinery.
There are numerous instances where it is expedient to separate gas-liquid mixtures, for example, where the gas is required to be separated from a "mist" of fine liquid droplets either because of considerations of environmental cleanliness or because one or both of the component parts of the mixture need to be recycled. It will also be expedient in many instances to separate gas-liquid-solid mixtures (e.g. including solids which are wear products of rotating machinery) and/or gas/vapor mixtures, e.g. mixtures of air and a hydrocarbon vapor. Such mixtures, which can include liquid and solid particles and possibly vapor, are generically referred to as "polydispersed aerosols".
Filters are known which can bring about such a separation. In particular, coalescing filters are known in which a gas containing small suspended droplets of liquid such as oil or the like--commonly referred to as a "mist" is separated and the liquid is retained in the filter. Coalescing filters can be made from a variety of materials including glass microfibers, especially borosilicate glass microfibers. It has recently been proposed to surface treat the microfibers with a flurochemical or other material that imparts oleophobic and/or hydrophobic properties, and such treated coalescing filters may also be usable for present purposes. Coalescing filters are generally of annular or tubular shape and may be formed by molding or pleating sheets of microfibers. In the case of molding, in particular, it may be desirable to include a binder resin which also can modify the surface energy of the fibers, for example, an epoxy resin or a silicone resin or a mixture or resins, to optimize filtration efficiency. Coalescing filter elements are generally formed with a mechanical support structure, for example, a layer of expanded metal, in contract with one or both of the surfaces of the coalescing filter element, and having sufficient open area as not to interfere with the filter operation.
This invention is based on the discovery that the use of rotary coalescing filters can improve the separation of a gas-liquid mixture (including a polydispersed aerosol) with relatively low pressure drop across the filter, approximating to dry filter performance when the filter is rotated at a range of speeds. Such operating conditions may include cyclical duty in which rpm is varied and, at the higher speed of the duty range, liquid is centrifuged from the filter. The invention is useful especially in the case where a gas-liquid stream to be separated is urged through the filter from a predetermined direction.
UK Patent Specification No. 1508212 (Rolls Royce) shows a centrifugal separator for separating a suspension of a liquid in a gas which comprises a rotatable chamber, an inlet to the chamber for admitting the suspension and an outlet for the chamber in a radially outer part of the chamber, said outlet being separated from the inlet. An outlet for gas is provided in a part of the chamber disposed radially inwardly of the liquid outlet. A packing is provided within the chamber which comprises a relatively rigid matrix which is a metallic mesh formed by plating the metal onto a semi-synthetic open celled foam structure and subsequently removing the synthetic material. As will become apparent from the following discussion of the present invention, the gas flow path into the packing is axial rather than radial, and the packing material used is significantly coarser than the microfibrous materials contemplated by this invention.